Thermally stable propellant powders containing powdered polymeric materials and perchlorates



United States Patent 3,214,308 THERMALLY STABLE PROPELLANT POWDERSCONTAINING PDWDERED POLYMERIC MA- TERIALS AND PERCHLURATES Howard E.Rice, Elkton, Md., assignor to Thiokol Chemical Corporation, Bristol,Pa., a corporation of Delaware No Drawing. Filed Dec. 13, 1962, Ser. No.244,268 6 Claims. (Cl. 149-76) The present invention relates to novelcompositions of matter and more particularly to propellant powders whichare stable for extended periods of time at high temperature.

There has been a pressing need in the oil drilling industry forpropellants of high heat stability for the purpose of shattering andpiercing oil well casings. Numerous types of devices, commonly known asoil well gun perforators, have been developed for this purpose. Gunpowder and ball powder have been used in such devices, but they haveseveral serious deficiencies. Gun powder is relatively heat sensitive sothat upon being lowered to great depths, premature firing and the likehave occurred. The temperature of oil wells increases, of course, as thewell becomes deeper. Many wells are now at the 12,000 to 15,000 footlevel, where the temperature is in the neighborhood of 325-375 F.Presently the deepest ones are at the 26,000 foot level and showtemperatures of about 465 F. The compositions of the prior art areunstable at temperature above 250 F. and thus cannot be used withreliability. Furthermore, these compounds require the synthesis ofexpensive nitro substituted derivatives.

It is therefore an object of this invention to provide a novelpropellant suitable for use at high temperatures. A further object is toprovide a novel composition suitable for high temperature uses in oilwell perforators. A still further object is to provide a compositionuseful as a propellant and pyrotechnic ingredient for nose cones ormissile warheads.

The compositions of this invention are very stable at high temperaturesfor extended periods. A preferred composition, utilizingpolyacrylonitrile, has been stored at temperatures above 400' F. forseveral months and has exhibited no signs of decomposition orautoignition. These compositions also have a low impact sensitivity incomparison with compositions of the prior art. They likewise are simplerand cheaper to prepare, as they are physical mixtures and thus do notrequire synthesis of expensive nitro substituted derivatives.

The compositions of this invention can be conveniently prepared byadmixture of the ingredients. Preferred oxidizers are ammoniumperchlorate, lithium perchlorate, sodium perchlorate and potassiumperchlorate; while preferred fuels are polyacrylonitrile,polyacrylamide, poly- N-vinylcarbazole and phenol-formaldehyde polymer.For best results, the fuel and oxidizer are combined in toichiometricratio. However, other ratios ranging from 40-95 percent by weight ofoxidizer and -60 percent by weight of fuel can be used. In addition,burning rate modifiers such as ferric oxide, ammonium dichromate, copperchromite, and ammonium ferrocene sulfonate and anticaking agents such asfinely divided silicon dioxide can be added as desired.

The compositions of this invention differ from other propellants in thatthey are not cast and cured. The fuels used are extremely high molecularweight compounds and are so viscous that they'are considered solids.They can be powdered in a hammer mill, for instance. Further, theirviscosity does not decrease upon heating.

These compositions, when ignited by suitable means such as a squib,volatilize rapidly producing large volumes of gas rather slowly. Thecompositions do not melt before volatilizing. It is thereforeadvantageous to have as much surface area available as possible. Thefuel and oxidizer can be reduced in particle size by means of a suitableapparatus, such as a hammer mill. One fuel, polyacrylonitrile, asmanufactured, has a particle size ranging from 3 to microns. This iseminently suited for the purpose. The other fuels. and oxidizers must bereduced in size before they are used.

The fuel and oxidizer are stirred until a homogeneous mixture isobtained. The burning rate modifier and anticaking agent can be omittedaltogether without affecting the properties of the propellant. Afterstirring, the fuel and oxidizer remain as discrete particles rather thanthe fuel becoming crosslinked, as in standard propellants. Since thefuel is already essentially a solid, no curing agent is required. Asmall amount of plasticizer can be added to the mixture to aidpelletization, if desired. The amount of plasticizer added is dependentupon the end use of the composition and is easily ascertainable by oneskilled in the art.

After preparation, the composition is pressed into a cartridge or otherdevice, equipped with a squib, lowered into the well and fired. Thereare several squibs, qualified at high temperatures, available for thispurpose. One such squib is obtainable from E. I. du Pont Company and isknown as the 8-95 squib.

It will be apparent to those skilled in the art that many modifications,both of materials and methods, can be practical without departing fromthe invention. The following examples are illustrative only, and are notto be construed as limiting the invention either in spirit or in scope.In these examples temperatures are given in degrees Fahrenheit F.) andamounts of materials in parts by Weight.

Example 1 A mixture of 12 parts of powdered polyacrylonitrile, 87 partsof ammonium perchlorate, 0.5 part of ferric oxide, and 0.5 part offinely divided silicon dioxide is stirred in a vertical planetary mixerfor 30 minutes. A cover is placed over the mixingbowl so that the finelypowdered material does. not escape during mixing. The mixture i checkedvisually to see that it is homogeneous. The propellant composition isthen removed from the mixer and either placed in a tool or stored untilneeded.

These compounds have been tested for their ability to power deviceswhich are used to pierce oil well casings at elevated temperatures. Forexample, this composition was placed in a cartridge and fired with asquib in wells 13,500 feet deep. The temperature was recorded at 350-360 F. and the tool was in this environment for periods up to one hour.No misfirings occurred. This composition has been held at 400 F. for onemonth and has shown no signs of decomposition or autoignition. Itsautoignition temperature is about 520 F.

Example 2 Following the procedure described in Example 1, the followingpropellant formulations are obtained.

No. 2 No. 3

Polyacrylamide powder Poly-N-vinylcarbazole powder Phenol-formaldehydepowder Lithium perchlorate Sodium perchlorate Potassium perchlorate.--Ferric oxide Silicon dioxide What is claimed is:

1. A propellant composition stable to autoignition and deformation attemperatures above 325 F., said propellant composition being anadmixture of about 5 to 60 percent by weight of a thermally stable fuelbinder, said fuel binder being selected from the group consisting ofpolyacrylonitrile, polyacrylamide and poly-N-vinylcarbazole, and 40 to95 percent by weight of a solid perchlorate oxidizer, and up to 5percent by weight of burning rate modifiers and anticaking agents.

2. A method of stabilizing propellant containing solid perchlorateoxidizer toward autoignition and deformation at temperatures above 325F. comprising the steps of adding to said propellant containing solidperchlorate oxidizer component, burning rate modifier, anticakingcomponent and the like, from about 5 to 60 percent by weight of athermally stable fuel binder component, said thermally stable fuelbinder being selected from the group consisting of polyacrylonitrile,polyacrylamide and, poly- N-vinylcarbazole and admixing said propellantcomponents until a uniform and homogeneous propellant composition isproduced.

3. A method of stabilizing ammonium perchlorate based propellants towardautoignition and deformation at temperatures above 325 F. comprising thesteps of adding to 40 to 95 percent by weight of ammonium perchlorateoxidizer component from 5 to 60 percent by weight of polyacrylonitrilefuel binder, and admixing said mixed components until a uniform andhomogeneous propellant composition is produced.

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4. A propellant composition stable to autoignition and deformation attemperatures above 325 F., said propellant composition being anadmixture of about 5 to 60 percent by weight of polyacrylonitrile fuelbinder, and to 95 percent by weight of ammonium perchlorate oxidizer,and up to 5 percent by weight of burning rate modifiers and anticakingagents. I

5. A propellant composition stable to autoignition and deformation attemperatures above 325 F., said propellant composition being anadmixture of about 5 to percent by weight of polyacrylonitrile fuelbinder, and 40 to percent by weight of potassium perchlorate oxidizer,and up to 5 percent by weight of burning rate modifiers and anticakingagents.

6. A propellant composition stable to autoignition and deformation attemperatures above 325 F., said propellant composition being anadmixture of about 5 to 60 percent by weight of polyacrylonitrile fuelbinder, and 40 to 95 percent by weight of lithium perchlorate oxidizer,and up to 5 percent by weight of burning rate modifiers and anticakingagents.

References Cited by the Examiner UNITED STATES PATENTS 1,700,085 1/29Scott 149 s3 11,964,222 6/34 Scott 149 s3 X 2,931,437 4/60 Smith 149-76CARL D. QUARFORTH, Primary Examiner.

1. A PROPELLANT COMPOSITION STABLE TO AUTOIGNITION AND DEFORMATION AT TEMPERATURES ABOVE 325*F., SAID PROPELLANT COMPOSITION BEING AN ADMIXTURE OF ABOUT 5 TO 60 PERCENT BY WEIGHT OF A THERMALLY STABLE FUEL BINDER, SAID FUEL BINDER BEING SELECTED FROM THE GROUP CONSISTING OF POLYACRYLONITRILE, POLYACRYLAMIDE AND POLY-N-VINYLCARBOZOLE, AND 40 TO 95 PERCENT BY WEIGHT OF A SOLID PERCHLORATE OXIDIZER, AND UP TO 5 PERCENT BY WEIGHT OF BURNING RATE MODIFIERS AND ANTICAKING AGENTS. 